Inverting/non-inverting Op-amp Inputs !!!help!!! - diyAudio
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Old 7th May 2002, 02:16 AM   #1
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Default Inverting/non-inverting Op-amp Inputs !!!help!!!

COnsider this circuit. A typical op-amp like conifguration. Could someone PLEASE explain to be which input is the inverting input and which is the non inverting input based upon which leg you take from the diff-amp???

I have seen circuit examples but I want an explanation. Thanks in advance!
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Old 7th May 2002, 02:18 AM   #2
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Another question. Where is the best place to put DC offset trim? is R5 correct for this?

Thanks again in advance
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Old 7th May 2002, 10:55 AM   #3
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Yes, R5 will trim the DC. With the input on the base, the collector output is inverted. Thus, if the base of Q2 is hooked to the collector of Q3, the output of Q2 is non-inverting when Q3 is the input. If Q4 was the input and Q2 hooked to its collector then the output of Q2 would still be non-inverting. If Q4 was the input and Q2 was hooked to Q3 the amp would be inverting. If Q3 was the input and Q4 hooked to Q2 the output would be inverting. For $6 AudioXpress will sell the Pass A40 circuit board which will allow you to experiment with this circuit. Or build an amp. I built a 250W/ch amp with a pair of these.
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Old 7th May 2002, 11:17 AM   #4
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Why have you placed r1 and r2 on the collector of Q1 and Q2?

Sonny
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Old 7th May 2002, 10:17 PM   #5
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Probably the take off point for driving Q23 should be
below R1 or R2.

The non-inverting input will be the one whose collector
drives the base of Q23
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Old 7th May 2002, 10:37 PM   #6
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Nelson pass wrote : "The non-inverting input will be the one whose collector drives the base of Q23"

Listen to him.

For r1 and r2, put them somewhere more usefull .. On the emitter of Q1 and Q2 to balance the currentmirror.

Sonny
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Old 7th May 2002, 10:49 PM   #7
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Default Typical design

IIR, if you check my monster phono amp or my monster headphone amp you can get some idea of differential stages and design of a discrete opamp.

http://home5.swipnet.se/~w-50719/hifi/qsxm2/index.html

http://home5.swipnet.se/~w-50719/hifi/qrv01/index.html
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Old 8th May 2002, 02:48 AM   #8
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Default So...

If I understand correctly this circuit is correct:


The current mirror is what threw me off.
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Old 8th May 2002, 02:50 AM   #9
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BTW:


What is the website for that audio express website???



Thanks
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Old 8th May 2002, 03:06 AM   #10
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You might want to increase the value of R6. I hope this is not supposed to be a power amplifier.

Jocko
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